1The sustainable management of material resources has given rise to numerous studies that public policies draw on. Yet certain aspects are insufficiently investigated or elucidated, making public strategies less clear and consistent. On the one hand, the description of material cycles is usually based on flows and stocks, not on the underlying variation of flows (growth in consumption and production). On the other hand, the purpose assigned to recycling and waste reduction in the system dynamics is often poorly clarified: for instance, is waste production reduction to be understood in the regulatory sense (including waste that benefits from recycling), or in the environmental sense (only waste discharged in landfills or the natural environment)? Should the aim be to decouple economic growth from total raw material consumption (primary + recycled), or from primary raw material consumption (only what is extracted from natural deposits)?

2In Europe, there are three EU strategic lines which, followed together, may prove contradictory:

• strengthening and increasing European industrial activities (COM, 2007),

• moving towards a circular economy, i.e. a “recycling society”, (EU, 2008), based first and foremost on recycled or re-used materials,

• giving priority to reducing quantities of waste rather than recycling (EU, 2006; EU, 2008).

3How does one develop a waste-based industry while proclaiming the ambition of a “zero waste” society, i.e. one deprived of the resource? How does one develop a circular economy while only granting recycling a secondary role? Finally, how does one close the loop while aiming at breaking it?

5In the following sections, we will tackle these issues with three objectives in mind:   

• establishing the physical conditions for sustainable material growth

• in order to do so, including material consumption growth in modeling a circular economy

• proposing a hierarchy of public priorities in the area of sustainable management of raw materials that are compatible with economic development.

6For that purpose, we will first examine the usual criteria for sustainable non-renewable raw material management; we will then take note of the acceleration induced by the constant growth in raw material consumption. We will next analyse the mechanical impact of recycling on non-renewable resource depletion, on the basis of a constant growth rate in raw material consumption. We will then deduce the criteria for sustainable material growth, and propose a few key factors for the sustainable management of non-renewable materials.  

1. Sustainability criteria for the management of non-renewable materials

7The quantity of mineral resources accessible to humankind gives rise to endless debate. The data relating to reserves are an industrial concept that fluctuates according to recent global production on the one hand, and to mining industry investment in prospecting and innovation on the other (Koroshy & al., 2010). However, even if technological advances can facilitate access to resources that are less and less concentrated, the economic and environmental cost of marginal resources is ever increasing. It is therefore in the general interest to delay resorting to these more costly resources as much as possible (Norgate & al. 2006).

8The sustainability of non-renewable material management is mostly approached on the basis of the following principle: “Consumption of non-renewable resources should be limited to levels at which they can either be replaced by physically or functionally equivalent renewable resources or at which consumption can be offset by increasing the productivity of renewable or non-renewable resources.” (von Gleich, in von Gleich & al, 2006).

9We will study in particular the strong sustainability model established by Ekins (Ekins, 2000) illustrated in figure 1. In this model, efficiency in the use of the resource (e) applies to the whole stock of as yet non-extracted material (S), to in-use stock (C) as well as to existing renewable substitutes (R), and the sustainability criterion is imposed on the material flow (w) which leaves the economic system to be dispersed or as ultimate waste. For the economy to be sustainable, the flow must at least be offset by improved efficiency in material use and by an increase (a) in the resort to a renewable substitute (R:

10w₀ ≤ (1 – e₀/e₁)(S₀ + C₀) + (a₀ – e₀/e₁)R₀ (subscripts 0 and 1 indicate two successive periods).

11The result of the formula, “strictly in accordance with the principle of strong sustainability, is to ensure that the stock of the given resource, together with any substitute that may have been developed, maintain their capacity to perform the relevant environmental function at its current level. The disposal of the resource is only sustainable if technical advances enable the stock remaining (plus substitutes) to perform the same level of function as the initial stock” (Ekins, 2000).

12This type of model is highly useful for a theoretical analysis of the sustainability of the materials economy. It does however have four theoretical, and above all practical, limitations:

• It considers the total concentrated material capital as equivalent from the point of view of its economic and environmental function, and therefore de facto neglects the irreversible nature of the continuous move of materials from S to C.  

• Its assets-based approach, compared to the relative hugeness of non-extracted resources S for most non-renewable materials, means it has no impact on the real economy.

• It is based on the marginal variation of the economic and environmental efficiency of the use of the resource e which is marked by such an uncertainty that it cancels out the practical efficiency of the approach.

• It is a static model which does not take into account the growth in total material consumption linked to economic growth.

13First,the modeldefines sustainability exclusively on the basis of material discharge. In this approach, it is important that each generation hands over to the next one a total concentrated raw material capital with an economic and environmental function equivalent to that which it enjoyed itself, whether in the form of in-use material, virgin material still to be extracted or renewable substitutes. It is therefore important essentially that it only dispersed (or lost, or wasted) that raw material in proportion with the improved efficiency it was able to apply to the actual or potential use of the total concentrated material stock. However, available materials in use or to be extracted do not all have the same value; in the case of demographic growth in particular, in-use material stocks need to be increased, all other things being equal. The impact of continued population growth or of increased average individual material wealth is not included in this purely environmental model which focuses on dispersion: ultimately, if society produced no waste but constantly increased its in-use material capital, it would eventually experience complete depletion of the to-be-extracted stock; yet, on the eve of this shock, the model still describes it as sustainable in the sense of material capital preservation.  

14Thesecond objection is that if the stock of non-extracted material S is very large compared to annual consumption, and, even more, to annual disposal w; a minute annual improvement in economic and environmental material efficiency would be enough to describe any economy as sustainable. In Appendix A, we show that in the case of iron, an annual productivity increase of 0.09% is enough for its present global economy to be deemed sustainable. Is it realistic and of practical significance, considering that global iron ore consumption rose from 1.1 billion to 2.2 billion tonnes between 1998 and 2008? (USGS, 2009)

15The third limitation of the model is that it essentially bases the determination of an actual statistical value, w, on the multiplication of a very large number, S+C, by a very small number, 1 – e₀/e_1,. whereas both are marked by considerable uncertainties: uncertainties as to the evaluation of concentrated raw material stocks still to be extracted from the Earth’s crust, and as to defining the relevant parameter for the economic and environmental efficiency of the use of the material.

2. Presentation of the model

18In this article, we will take steel as the main example since it is the most consumed, the most recycled, and probably the most documented metal in the world.

19Global raw steel production increased thirtyfold in the 20^th century, i.e. an average increase of 3.5% per annum that is roughly exponential. For other metals, developments in annual production are sometimes influenced by technological changes, regulatory modifications, or the dynamics of consumer markets. However, there is in fact an exponential trend, in slices of several decades, between two major market changes (Grosse, 2010). In the rest of this article, we will therefore consider that raw material production trends are exponential, i.e. with a constant annual growth rate, at least in slices of several decades.  

2.1 Net addition to stocks

20In order to model variation of in-use stocks and material flows in the economy, we must consider the balance of inputs and outputs in the economy. At a given time,

• raw material is consumed

• waste is discharged

• stocks of in-use material are built up or reduced (inputs and outputs in the “use” part of the diagram in figure 1).

21In general, the flow of discharged waste is lower than that of consumed material since part of the material is stocked. Conversely, if an economic actor reduces his or her material goods (by clearing the attic and taking everything to the waste collection centre), the waste flow is temporarily higher than that of consumed material. We have the following balanced relationship:

22Material consumption = Waste discharge + Net addition to stocks

23Net addition to stocks is defined as the difference between material added to stocks and material removed from the stock to be discharged as waste. The difference is usually positive.

2.2 Residence time

24We can establish the link between the flow of net addition to stocks and residence time in the economy. Average residence time is the average time separating production of a raw material in a form usable by industry and its discharge as waste after manufacture, distribution and use; therefore it is the time interval between two equal values in the curve for changes in total raw material consumption on the one hand, and the curve for changes in the quantity of that material in the total amount of waste on the other (figure 2). If total production of a raw material grows at a constant annual rate (exponential profile of production), and if shareσ of the production devoted to net material stock increases is constant, then residence time can be expressed as follows:

25Where:   rt is the residence time in the economy of the material under consideration

26a is the annual growth ratio in raw material consumption (1 + growth rate)

27σ is net addition to stocks, i.e. the proportion of total raw material consumption devoted to net stock increase,

28ρ = 1 – σ is therefore the waste output ratio of the economy, i.e. the relationship between waste flows (recycled and non-recycled) and raw material consumption of a given material.  

2.3 Examples

30Figure 2 shows the link between residence time and net rate of addition to stocks: for the same consumption profile, the longer the residence time, the more consumption growth results in addition to stocks; or again, the more material stock in the economy increases, the longer its average residence time.

31With no claim to exhaustivity, three examples clearly illustrate, in three major areas of the “material assets” of a developed country – namely France – that the proclivity of our society to increase stocks is quite significant:

• • 6   Source: INSEE, 2010
  • 7   Source: Comité des Constructeurs Français d’Automobiles, 2010
  • 8  A complete picture would require taking into account second-hand car imports and exports, which ho (...)

  cars: from 1996 to 2008, 20% of the new cars registered added to the total number of cars, i.e. produced a net increase in in-use stock (whose average unit weight did not fall over the same period)678,

• • 9   Source: Ministère de l’écologie, de l’énergie, du développement durable et de la mer, France, con (...)

  housing: from 1970 to 1996, the mean housing surface per capita rose from 22 m² to 35 m² on average9 i.e. an increase of almost 60%, to which should be added population growth of about 0.5% per annum (Daguet, 1996),

• • 10  The annual increase in surface area covered by landfills in France can be evaluated at 1 to 1.5 km(...)

  artificialised land: from 2000 to 2006, artificial land in France expanded by 120 km²/year, confirming a long-established trend already measured in the previous decade10 (Pageaud & Carré, 2009).

32This suggests the hypothesis that our consumer society, far from being exclusively a society of disposable objects, is just as much a society of accumulation: increased wealth not only serves to consume what is short-lived, or intangible, but also to add significantly to our individual and collective ownership of material goods.

2.4 The role of recycling in resource preservation

33Recycling non-renewable raw materials avoids carrying out two technical operations;

• disposing of them in landfills as waste on the one hand;

•  producing an identical quantity of primary raw materials from ore on the other.

34The environmental impact of the primary material chain is to a large extent global and cumulative over time: this is true for climate change, and also for pollution and biodiversity erosion induced by extraction; it is also true, to a certain extent, for the decrease in arable land surface areas.

35Assessing the environmental impact of recycling in the first analysis is therefore equivalent to assessing the depletion of primary resources it prevents.

36How can recycling contribute to the sustainable management of natural resources? We previously modelled the possible impact of recycling when material growth is exponential (Grosse, 2010). The main conclusions of this work are:

• The influence of recycling on resource preservation is negligible for any raw material with a greater than 2% per annum increase in world production.

• It is only if the annual raw material consumption growth rate is below 1% that recycling has a significant positive impact. It can then provide over one hundred years of respite.

• However, relative decoupling of the economy is not enough: a growth rate in total material consumption below 1% is insufficient on its own, and, in addition, requires a very high recycling rate (more than 60 to 80%) in order to delay significantly the resource depletion rate.  

• The time shift for cumulative consumption is highly sensitive to the growth rate of total material consumption (primary + secondary). The slower the growth, the more recycling contributes to “buying time” before resource depletion.  

• Recycling has a higher impact if material residence time in the economy is short; conversely, its impact is smaller for a long residence time.

• Finally, the impact of recycling must be analysed in relation to present economic parameters (as trends), not on the basis of an assumed future slowing down of consumption. As a whole, the relative impact of cumulative present-day recycling becomes negligible after a few decades in view of global production growth.

2.5 The effects of stocks and waste flows

37In the above analysis, the reasoning was based on the assumption that the average residence time of materials in the economy was a stable value. This parameter is directly connected to the flow of net addition to stocks, this itself being equal to the difference between the raw material consumption flow and the waste flow for a given material (see figure 2). The average residence time in the economy is not a lever for economic and political action. This is not the case for its two underlying flows:

• The total consumption of a raw material (primary + recycled) is the main parameter of our analysis, and an obvious economic parameter.

• The waste output flow (dispersed + recycled) is also commonly measured and analysed and is currently the subject of policies of the quantitative type, aiming for instance at reducing through prevention volumes of waste produced by households and companies (EU, 2008).

38After examining the conditions for quantitatively sustainable management of non-renewable resources in relation to the consumption growth rate and their recycling efficiency, we can add the influence of a third parameter, which is the raw materials output ratio of the economy (ratio between the quantity of a raw material discarded in the form of waste and the quantity simultaneously consumed by the economy).

39By replacing residence time with its relation to the waste output ratio of the economy (ρ), in the previously established equations (Grosse, 2010), we find the following three new equivalent relations:

40

41We established above that, in any event, there is no such thing as sustainable management of raw materials unless its production growth rate is less than 1% per annum. The graphic representation of the cumulative consumption shift of a raw material obtained for various recycling rates, as a function of the waste output ratio in the economy, evidences the viability domains of sustainable growth (in this case for a growth rate of 0.5% per annum) (figure 3).

42If 60% of the material present in waste is recycled globally, and the equivalent of 80% of the global consumption of the same material is discharged constantly in the form of waste, recycling delays by 130 years the scarcity endpoint of the resource. However, if, thanks to waste prevention measures, quantities of the material discarded as waste are brought down to 50% of consumption, all else being equal, the effect of recycling falls to only 70 years, and even a recycling rate of 90% would fail to reach the 130 years previously gained.

43Therefore, gaining 100 years before depletion of a resource through recycling is impossible if the waste output ratio of the material concerned is less than 50% of its total production. It is only with output ratios above 80% that it becomes possible to delay significantly raw material consumption and depletion. The phenomenon becomes more pronounced as the growth rate increases. With equivalent raw materials consumption, discharging less waste means depriving recycling of part of its resources. Necessarily, this leads to drawing more massively on primary resources in the Earth's crust.

44For instance, the International Panel for Sustainable Resource Management estimates the average residence time in the economy for steel to be 25 or 40 years (UNEP, 2010). In view of the underlying growth rate of global production during the last century (3.5% per annum), this time range reflects a net addition rate to stocks of 61 to 75% (waste output ratio of only 25 to 39%). In such a situation, even with a lowering of growth in steel production to 0.5% per annum (almost zero-growth), a recycling rate of 60% or 70% would only buy 30 to 60 years, and recycling 90% of the metal contained in waste would only lead to 50 to 80 years of consumption shift (see figure 3).

3. The key to sustainable management of non-renewable resources

3.1 This model’s limitations

45The approach we have used neglects the innate complexity of recycling, in particular as regards the progressive deterioration of the material’s properties (downcycling), which has been modelled through changes in the entropy of the material system (Gößling-Reisemann, in Von Gleich & al. 2006).  This observation, however, does not affect the validity of our analysis, since downcycling is interpreted in this case as one of the technical limitations to overcome if we are to achieve a high recycling rate.

46Nor does our analysis claim to respond to Jackson’s ambitious and pertinent issue of “prosperity without growth” (Jackson, 2008).  As Ekins points out, “in one sense, any level of use of non-renewable resources is unsustainable” (Ekins, 2000).  In consequence, a “permanently sustainable” economy cannot, to be perfectly honest, rely essentially on material growth.  However, our analysis does respond to Jackson’s invitation to work on a transition towards a sustainable economy and to set environmental limits on human activity, in the shape not of theoretical criteria, but of criteria related to the economy’s statistical values.

3.2 Quasi-circular growth

47Our analysis does reveal several important facts.  It determines a middle course, and therefore a pragmatic one, between the uncontrolled industrial expansion of the 20^th century and the still extremely virtual target of achieving material degrowth on a global scale.  While we are realistic in accepting the need for economic growth and the still existing coupling between wealth creation and material consumption, we demonstrate that it is possible, if certain conditions are met, to control in the long term the gradual depletion of concentrated deposits of the principal metals and related environmental impacts.

48We can summarise the three cardinal virtues of sustainable material growth (figure 4), in other words, describe the profile of a sustainable economy which does not rely on a decrease in the need for raw materials:

• Material growth must be less, or even considerably less, than 1% per annum (growth rate of global production of each raw material, primary + recycled).

• The recycling efficiency rate must be greater than 60%, or even 80% (proportion of material contained in waste which is actually recycled).

• The rate of addition to stocks must be less than 20%, meaning that the economy must discharge as waste at least 80% of the quantities of each material it consumes.

49The path is narrow and challenging, demanding a strict balance between three fundamental parameters, failing which it would simply become impossible to find a solution to the problem of sustainable management of non-renewable resources.

4. Evaluation of public policies for the sustainable management of non-renewable resources

4.1 Criteria for the evaluation of sustainability and a quasi-circular economy

51These three parameters are three levers for action, and they are, to a considerable extent, independent of each other and precisely defined. They make it possible to evaluate sustainable management policies of non-renewable raw materials (table 1).  In Appendix B, we have shown how they determine the development scenarios of non-renewable resources consumption.

TMC : Total Material Consumption: measures the total material use associated with domestic production and consumption activities, including indirect flows imported but less exports and associated indirect flows of exports (OECD, 2008). Flows of recycled material in the economy are not included. To arrive at the total consumption of raw materials (primary + recycled), Domestic Recycling must be added to TMC.

4.2 A complement to the traditional environmental approach

52Environmental approaches to the sustainability of the raw materials economy are based on an analysis of extraction and discharge events in the natural environment.  The flows they include are mainly the consumption of primary raw materials and the disposal of ultimate waste (i.e. which is returned to the natural environment); recycling flows being regarded as internal to the economic system, only passing interest is shown in total raw material consumption or total waste flows, i.e. which include recycled materials.  We have, however, shown that such approaches cannot be the sole basis for public or industrial priorities, since they neglect the part played by consumption in the dynamics of the economy: economic growth stems from the consumption of both primary and secondary raw materials so that its actual dynamics are not realistically modelled if only primary consumption flows are analysed.  Our approach underlines the decisive importance of observing total raw material consumption (TMC+DR) and its growth when analysing the sustainability of the raw materials economy.

53For example, an observation of the curves for global consumption of primary lead reveals a slight underlying drop between 1970 and 1995, and gives the impression that an absolute decoupling of the economy occurred; but when the cumulative curves for the consumption of both primary and secondary (recycled) lead are observed, it becomes clear that this was not the case at all.  Throughout this period, with the brief exception of five years before 1995, global lead consumption never ceased to increase, albeit slowly, and the drop observed in the consumption of primary lead over two decades was simply the transitory effect of a gradual increase in the recycling rate.  It could therefore only be short-lived, until recycling rates stabilised at a higher level, as resumed growth unfortunately confirmed in the first years of this century (Grosse, 2010).

4.3 Public priorities as regards material cycles

54Our approach also responds to the question raised on the subject of European policies in the introduction to this article.  While the solutions to be implemented to encompass the three criteria remain to be defined and will anyway be complex, their logic and priorities are now perceptible.

56A second weak point is that they mostly rely on waste management for material management, which triggers perverse effects or illusions:

• the illusion that recycling on its own could play a key role in the conservation of deposits and in the reduction of primary consumption environmental impacts, whereas it is almost useless in the absence of any slowing down of total material consumption growth;

• the illusion that an effort to reduce waste generation would lead automatically to slowing down material growth, whereas it is just as prone to having the perverse effect of increasing material accumulation.

• On the one hand, waste prevention in the meaning of the European Directive mixes together several different concepts, i.e. firstly waste reduction at source, secondly material preparation for re-use (which de facto prevents it from becoming waste), and finally reduction of harmful effects and content in harmful substances in waste.  While the last two are amply justified for efficient material management, the first concept cannot, as we have already noted, be left as it is.

• On the other hand, the concepts of prevention and preparation for re-use are not in the same category as the other items in the waste hierarchy set out in the Directive, which are technical waste-processing procedures.  Their position in the waste hierarchy generates confusion in the implementation of public policies.

58The European Directive on waste could therefore move forward in the following way:

• Focusing waste hierarchy on materials-processing procedures for materials once they have become waste, and clearly positioning recycling as a first priority.

• Giving prevention policies full public priority, separate from waste hierarchy, and attaching to it its own prevention hierarchy:

• Preparing materials and products for re-use

• Preparing materials and products for recycling

• Avoiding the production of waste that cannot be recycled, i.e. waste in the environmental sense of the word, more restrictive than the legal meaning, (see box)

• Preparing materials and products with a view to reducing the harmful effects of waste on the environment and on human health  

• Preparing materials and products with a view to reducing their content in harmful substances.

59A more ambitious version should include, in some form which remains to be defined, an attempt to decouple wealth from raw material consumption (both primary and recycled) on the one hand, and to find a way to control in-use stock growth on the other.  The quantified objectives which are the outcome of our analysis could guide such policies, sector by sector, for each material.  To this end, the Directive on waste would need to evolve into a Directive on raw materials.  That being done, recycling would access the status it deserves as a result of this analysis: a raw materials industry just as much as a waste industry, so that new opportunities would be on offer for public policies aiming to favour recycling.

60 For example, in many countries, public policies set as a target a given recycling efficiency rate for certain categories of waste (EU 2008). This is problematic because the waste industry then faces alone the challenge of creating the market for the additional recycled materials, while the production industry does not absolutely need to buy it instead of primary raw materials. Furthermore, whatever the ambition of the target, our analysis shows that such efforts to achieve a quasi-circular economy by concentrating on the waste side (output) of the materials cycle are vain, as long as one does not work simultaneously on the production side (input) of the cycle. It would be therefore much more efficient for public policies and regulations to set as a target a given proportion of input material in any new good that should come from recycling rather than from primary production. Driving public policies by the input proportion coming from recycling in new goods production would influence at the same time both the recycling efficiency rate of waste management (by fostering a market demand for recycled materials) and the speed of growth of materials production and consumption (under the constraint of keeping pace with recycling in order to achieve the required proportion of input materials).”

61Our observations require that further attention be given to the waste output ratio criterion.  It should not be understood as an incitement to produce a greater volume of waste, but as identifying net addition to stocks as the true lever, that is to see to it that in the future, consumption of raw materials should only slightly exceed discharges in the form of waste. The systems to be implemented are still to be defined, but possible solutions will not be wanting.

5. Conclusion

63For the industrial world, this approach offers two clarifications: on the one hand, guidelines contributing to community reflection on public policies favouring sustainable economic development; on the other hand, indications regarding the direction in which economic models could be encouraged to move, and the new services of the “green economy” that could be associated in the future to material and waste management.  One of the conclusions is that it will be increasingly difficult to consider waste management as an isolated industrial sector.  On the contrary, it must gain an ever-increasing role in an integrated approach of the material cycle as a whole.

6. Glossary

64Waste: The concept of “waste” has two different meanings, depending on context: for environmentalists, waste is the material that leaves the human system for final dispersion or discharge into the environment or landfills; for lawmakers, industry and consumers, waste is the material that an economic actor gets rid of, whether it is eventually dispersed or recycled in the economy. For instance, according to European regulations, waste means “any substance or object which the holder discards or intends or is required to discard” (Directive 2008/98/EC on waste). In this article, unless otherwise stated, waste should be understood in the legal and usual acceptance of the word (see figure 1).

65Material Consumption, Raw Material Consumption, Material Growth: Refers here to total flows of consumption of a given raw material, adding both primary (extracted from earth) and recycled raw material (sometimes called secondary raw material).

66Recycling Efficiency Rate: It refers to the actual efficiency of the process of waste recycling, i.e. the proportion of a given raw material waste which is recycled. This is different from the apparent recycling rate which is the proportion of raw material consumption (see above) which comes from recycling.